1. Field of the Invention
This invention pertains to the field of video switching systems and more particularly to a video switching system for selecting a video signal from a plurality of video channels comprised of independent modular units which may be cascaded to increase or decrease the number of video channels as desired by a user.
2. Description of the Prior Art
Prior art systems for switching video signals from a plurality of video input channels to one or more monitors used for viewing the video signal have consisted of integrated switching systems adapted to the particular number of video channels used in the video system. Such video switching systems are often used in CCTV surveillance systems, in which the video signals originate from surveillance cameras. Video switching systems, however, also find application in other fields in which a plurality of video signals are to be switched such as in television studios or editing of video signals originating from pre-recorded and live sources. Also the end destination of the switched signal can include devices other than monitors, for example, video tape recorders (VTR) or broadcast transmitters.
Up until now, video switching systems have been available having a predetermined number of video inputs, usually 4, 8, 12, etc. If the surveillance installation included 6 cameras of which it was desired to be able to scan from each camera in a selected sequence, a switcher having 8 inputs and at least one output was required. The switch would have to be altered to accept 6 inputs. If at a later date a user of the video security system desired to increase the number of surveillance cameras to, for example, ten, it was necessary to completely replace the eight channel switcher with a twelve channel switcher, at a consequent financial loss.
Individual CCTV installations have differing requirements. Most such video security systems are used in industrial and commercial environments and the number of cameras needed is dictated by the nature of the installation. Should the owner of the installation decide to alter the premises to expand or decrease the number of areas for which surveillance is needed, prior art switching systems required the complete replacement of the video switching unit to accommodate changes in the number of cameras since they lacked the flexibility to be used in a system having a number of video inputs different from that for which they were designed.
Due to this lack of flexibility, it was necessary for a manufacturer to make, and a distributor to stock, a large number of different switching units each tailored to a specific installation. Consequently, the cost of the resulting switching unit was necessarily higher, due to the additional engineering time required to design a large number of units, the added expenses for the maintenance of a larger inventory (both by the distributor and the manufacturer) and the increased manufacturing costs since production efficiencies are not as easily realized by a large number of small production runs as in a large production run of a single item. These costs were, of course, passed on to the purchaser, and raising the cost of an installation commensurately.
Additionally, since in most prior art systems the video switching device is designed for a particular installation and is one integrated unit, failure of any section of the circuitry would often necessitate shutdown of the entire system for repair. In the present invention, the modular nature of the video switcher permits the removal of a single module if it fails. Thereafter, the system may be repaired simply by the removal of the failed module which can then either immediately be replaced or taken out for repairs, while permitting at least a portion of the surveillance system to remain in service.
It is often necessary to remotely control the operation of the surveillance camera from the remote console in the monitoring area. In conventional video switchers individual camera controls are provided for each remote camera. Thus, individual iris, pan, tilt, zoom and focus controls might be included for each camera at the remote console to control these functions. This results in a very bulky system having a very large number of controls. Such systems are not only inconvenient for an operator to use, but also require a large amount of mounting space which is not always readily available in the monitoring area.
It is thus an object of the present invention to provide a video switching system that is expandable to accept any desired number of video inputs.
It is a further object to provide a video switching unit that can be assembled from a plurality of identical or nearly identical modules which can be cascaded when the user's needs change.
It is yet another object to provide a flexible, complete, video switching system which is inexpensive to manufacture and requires a minimum of space.
These and other objects of the present invention will become apparent upon reference to the following specification and annexed drawings.